Alteration in cell volume of vertebrates results in activation of volume-sensitive ion flux pathways. Fine control of the activity of these pathways enables cells to regulate volume following osmotic perturbation. Protein phosphorylation and dephosphorylation have been reported to play a crucial role in the control of volume-sensitive ion flux pathways. Exposing Amphiuma tridactylu red blood cells (RBCs) to phorbol esters in isotonic medium results in a simultaneous, dose-dependent activation of both Na +/H+ and K+/H+ exchangers. We tested the hypothesis that in Amphiuma RBCs, both shrinkage-induced Na +/H+ exchange and swelling-induced K+/H + exchange are activated by phosphorylation-dependent reactions. To this end, we assessed the effect of calyculin A, a phosphatase inhibitor, on the activity of the aforementioned exchangers. We found that exposure of Amphiuma RBCs to calyculin-A in isotonic media results in simultaneous, 1-2 orders of magnitude increase in the activity of both K+/H+ and Na+/H+ exchangers. We also demonstrate that, in isotonic media, calyculin A-dependent increases in net Na+ uptake and K + loss are a direct result of phosphatase inhibition and are not dependent on changes in cell volume. Whereas calyculin A exposure in the absence of volume changes results in stimulation of both the Na+/H + and K+/H+ exchangers, superimposing cell swelling or shrinkage and calyculin A treatment results in selective activation of K+/H+ or Na+/H+ exchange, respectively. We conclude that kinase-dependent reactions are responsible for Na+/H+ and K+/H+ exchange activity, whereas undefined volume-dependent reactions confer specificity and coordinated control.
- Cell volume regulation
- Phosphatase inhibitors
- Volume-dependent coordination of K loss and na uptake
ASJC Scopus subject areas
- Cell Biology